Among many emerging technologies developed to meet the increasing demand of high speed data transfer, MIMO is one of the most promising technologies. Unlike traditional techniques, such as a diversity technique which tries to mitigate multipaths, MIMO takes advantage of the existence of multipaths.
In a prior art MIMO system, multiple omni-directional antennas are typically placed at a transmitter and a receiver. To improve the MIMO system performance, multiple beam switched subscriber based smart antennas (SBSAs) are provided to replace omni-directional antennas at the transmitter, receiver, or both. The beam switched SBSAs may be switched parasitic antennas (SPAs), such as Trident or Delta type antennas, or phase-shift based beam selection antennas, such as those using a Butler matrix or a fast Fourier transform (FFT) matrix.
To support SBSA MIMO, physical layer information, such as a signal-to-noise ratio (SNR) and channel state information (CSI) is available. Even though this information is accessible from the physical layer, it requires internal bandwidth to exchange this information between the physical layer and a medium access control (MAC) layer. Therefore, it is desirable to use some explicit information at the MAC layer to support the beam selection in the SBSA MIMO system.